1. Field of the Invention
The invention relates to a subscriber's telephone speech and signalling circuit including an integrated circuit powered by the exchange battery via the subscriber's line, the power supply for the integrated circuit being maintained during line breaks by the charge on a capacitor which is charged from the exchange battery via the collector-emitter path of a transistor when the subscriber's line is looped and means for preventing the discharge of the capacitor through the transistor when a line break is detected.
2. Description of the Related Art
In such circuits the means for preventing the discharge of the capacitor has previously comprised a diode in series with the capacitor between it and the transistor. However although the diode adequately prevents the discharge of the capacitor it has the disadvantage of reducing the voltage available to supply the integrated circuit by its forward voltage drop thus limiting the length of line over which the circuit will operate.